1. Field of the Invention
The present invention relates to a ternary alloy thin film for use in the manufacturing of flat panel display and physical vapor deposition target used to produce such films. In particular, the film deposited on the glass substrate exhibits low resistivity and high hillock resistance.
2. Description of Related Art
Flat panel displays such as liquid crystal displays (LCD) are used in many applications such as television sets and notebook-type personal computers. To improve the image quality such as resolution and contrasts thin film transistors (TFTs) have been used as switching elements. TFTs are active devices comprising a semiconductor film formed on an insulating substrate such as a glass substrate and also includes electrodes made of metal films wherein the electrodes are connected to the semiconductor film.
In recent developments of LCDs, there is an increasing tendency toward a larger size panel and a higher resolution. As a result, it has been required to form the electrode film of the LCD of smaller dimensions. Such a reduction in dimension provides an increase in the electrical resistance of interconnections and electrodes. This results in an increase in delay time of the electric signals. To suppress the signal pulse delay caused by the reduction in size of the film electrodes in the LCD to a sufficiently low level to be applicable to color LCDs, and in particular to large-sized color LCDs having a panel size of 10 inches or greater, it is required that the electric resistivity of the electrodes of semiconductor devices be equal to or less than 5 μΩ cm.
As a result, the film used to form the electrode of a semiconductor device in the LCD must have various characteristics, inter alia, low resistivity and high hillock resistance. The resistivity of the material used to form the electrode film in the LCD has an influence on the signal transmitted. In particular, if a material having a high resistivity is used to form the thin electrode, then the high resistivity causes a reduction in the conduction speed of the electric signal and creates an increase in the signal pulse delay. Such a signal pulse delay is an important factor which determines the overall characteristics of the LCD. In large-sized and high-resolution LCDs, the low-resistivity is the most important factor to prevent the delay in the signal.
A reduction in hillock formation is likewise important. The material used to form the electrode film is subjected to temperatures ranging from 300° C. to 400° C. for 20 min to 30 min after the formation of the deposition of the film on the substrate and in the subsequent deposition of insulating film using plasma enhanced chemical vapor deposition (PECVD). When aluminum is employed, as the material to form the electrode in the LCD, small-sized hemispherical protrusions called hillocks are produced on the surface of the film during PECVD deposition of insulating film. The hillocks in the form of hemispherical protrusions are produced due to compressive stress caused by the difference in the thermal expansion coefficient between the glass substrate and the aluminum film. In TFT-LCDS, the electrode film is generally located at the bottom of the multilayer structure. Therefore, the hillocks on the electrode film make it impossible to form other films thereon in a flat shape. Furthermore, when an insulating film is formed on the electrode film, if hillocks are produced on the electrode film, the hillocks can protrude the insulating film and thus cause an electric short circuit (electric insulation failure) between layers.
Thus, in addition to low resistivity, the electrode film material in the LCD is required to have preferably no hillocks and whiskers or less than 0.5 μm hillock size formed during annealing. To address these issues a number of aluminum alloy sputtering targets have been suggested in the related art. For example, Onishi et al Effects of Nd content in Al thin films on hillock formation, J. Vac. Sci. Technol. A, Vol. 15(1997) is directed to Al—Nd films where the hillock density is strongly dependent on Nd content.
Yamamoto et al (U.S. Pat. No. 6,033,542) pertains to an electrode for semiconductor devices made of an Al alloy containing one or more alloying elements selected from Al, Co, Ni, Ru, Rh and Ir.
Hiroshi (Japanese Patent Document No. 10-199830) relates to a target material formed of an Al matrix structure containing one element selected among transition elements.
Onishi et al (Japanese Patent Document No. 2000-199054) pertains to an aluminum alloy sputtering target composed of aluminum matrix phases and intermetallic compound phases of aluminum and alloy elements on the grain boundaries between the intermetallic matrix phases.
Yoshikawa et al Spray formed aluminium alloys for sputtering targets Powder Metallurgy, Vol. 43 (2000) discloses fine, uniform microstructure sputtering targets of Al—Nd and Al—Ti material manufactured by spray forming.
Takagi et al (U.S. Pat. Nos. 6,096,438 and 6,387,536 B1) pertains to an Al alloy film for use as an electrode of a semiconductor device and an Al alloy sputtering target for depositing same.
Nishi et al (U.S. Patent Application Publication No. 2001/0004856 A1) relates to an aluminum or aluminum alloy sputtering target manufactured by spray forming and in which the maximum length of all the inclusions is 20 μm or less.
The drawbacks associated with the conventional thin film materials and the targets utilized to manufacture same, is that they do not satisfy the requirements needed to manufacture electrode films for the flat panel display.
To overcome the disadvantages of the related art it is an object of the present invention to eliminate a binary Al—Nd alloy and provide an aluminum ternary alloy film and sputter target used to deposit such film. In particular, the films deposited have a resistivity, preferably of less than 5 μΩ cm and high hillock resistance after the film is annealed.
Another object of the invention is to reduce the cost of aluminum ternary systems by reducing or replacing the second component (i.e., Nd) with rare earth metals such as Ce, Dy, Gd, and reduce the rare earth content by adding a less expensive third component.
It is a further object of the present invention to provide a novel manufacturing process for the sputter target, thereby reducing the number of requisite steps necessary to generate homogeneous and fine microstructure of said target.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings and claims appended hereto.